I. Field of Invention
This invention relates to low fusing nickel base alloys, particularly nickel base alloys which are useful for cast metallic structures for dental prosthetic devices or for cast jewelry. The alloys of the present invention are particularly useful for preparing cast structures in gypsum bonded investments.
Alloys of the general type with which the invention is concerned typically are characterized by their having resistance to corrosion in the oral environment, a tensile yield strength in excess of 40,000 psi, and good castability from temperatures lower than about 1,480.degree. C. For compatibility with gypsum bonded investments, these alloys typically have a solidus temperature lower than about 1,150.degree. C. and a liquidus temperature lower than about 1,260.degree. C.
Preferred nickel base alloys of this type typically contain 10 to 20 percent chromium and 0 to 8 percent molybdenum with lesser amounts of tungsten, vanadium, tantalum, niobium, tin, aluminum, manganese, boron, iron, silicon, cobalt, carbon, or berryllium or combinations thereof.
II. Description of the Prior Art
The nickel-berryllium system as a binary eutectic is disclosed in depth in U.S. Pat. No. 3,704,182 to Griffiths. This patent also described the mechanism by which chromium participates in the eutectic reaction, and the use of columbium, also known as niobium and referred to hereinafter as niobium or Nb, as a hardening element in combination with solution heat treating at 1,090.degree. to 1,175.degree. C. followed by subsequent age hardening heat treatment.
The enhanced corrosion resistance in nickel-beryllium alloys with the addition of chromium in the 10 to 20 weight percent range is disclosed in U.S. Pat. No. 1,945,679 to Corson. This patent further discloses that the substitution of molybdenum and tungsten for chromium can be accomplished while maintaining corrosion resistance.
U.S. Pat. No. 2,089,587 to Touceda makes use of the excellent castability and corrosion resistance of nickel-chromium-beryllium alloy systems of the type disclosed in the above Corson and Griffiths patents, and discusses the use of systems of this type for casting dental prosthetic articles. Further refinement of alloys of this ternary system for applications in dental devices is discussed in U.S. Pat. No. 2,631,095 to Griffiths, which shows that additions of manganese to the system could give further control of the melting range of the alloys and that cobalt could be substituted for nickel over a wide range of compositions. In the compositions disclosed in U.S. Pat. No. 3,464,817 to Griffiths, the improvement in mechanical properties by the addition of aluminum was demonstrated.
The addition of aluminum to a nickel base alloy also is suggested by U.S. Pat. Nos. 2,621,122 to Gresham, 4,292,076 to Gigliotti, 3,464,817 to Griffiths, 3,749,570 to Lyon, and 4,049,427 to Guerra, and by United Kingdom Application GB No. 2038359 to Unitek.
The manganese effect is disclosed in U.S. Pat. No. 2,631,095 to Griffiths. The effect of manganese on the melting range of nickel-chromium-beryllium alloys is utilized in U.S. Pat. No. 3,464,817 to Griffiths to produce alloys castable in gypsum bonded investments.
Gypsum bonded investments are generally known to be desirable for lost wax casting of dental prosthetics and items of jewelry because they can provide excellent replication of surface detail. The utility of gypsum bonded investments is reduced or lost as the melting range of an alloy system is raised so that the casting temperature must increase; conversely, lowering the melting range of an alloy system improves the ability to utilize gypsum bonded investments.